Teeth discoloration results from deposition of chromogenic substances called stains on the teeth, and this causes a serious problem in terms of aesthetic appreciation. As a means to remove stains, a common method is such that an oral composition such as a dentifrice composition containing a dental abrasive is held in the mouth using a tool such as a toothbrush, and the teeth are brushed. Because stains are removed mainly by abrasion, it is believed that a higher stain removal effect is achieved by the use of a dental abrasive having a higher abrasive ability. From this viewpoint, a harder dental abrasive would be preferable for the removal of stains, because a harder dental abrasive is considered to abrade the tooth surface with more physical strength and provide a high stain removal effect.
However, when an oral composition containing a dental abrasive having a high abrasive ability is used, there is a risk that the teeth may be abraded more than necessary. When the tooth surface is abraded, the dentine may be exposed, which may cause hypersensitivity. Further, because the exposed dentine has poor resistance to acid, tooth decay may be promoted. For example, alumina, i.e., a typical example of a hard dental abrasive, has an excellent stain removal ability, but also damages the teeth by abrasion. Although various improvements have been made to prevent damage to the teeth, the problem has not yet been solved. Today, oral compositions rarely contain alumina.
Therefore, there is a demand for the development of an oral composition having a high stain removal ability while having an appropriate abrasive ability; specifically, an oral composition having a high stain removal ability relative to its abrasive ability (i.e., the balance between the abrasive ability and the stain removal ability is good).
For example, Patent Literature 1 discloses that an oral composition comprising two types of silica having different abrasivities (silica with high abrasivity and silica with low abrasivity) as dental abrasives is useful to remove stains without damaging the teeth. However, this oral composition also contains highly abrasive silica, and thus has not exactly eliminated the risk of damaging the teeth.